1. Field of the Invention
The invention relates to a correlation detector for measuring distances and tacking images by calculating a correlation between two images.
2. Prior Art
Methods of tracing the locus of a moving object by calculating a correlation between two images are disclosed in, e.g., Japanese Patent Unexamined Publication Nos. 135587/1982 and 135588/1982. Conventional devices using such methods calculate the correlation by converting an analog signal of respective pixels into a digital signal, storing the converted digital signal, and causing their digital operation unit to directly multiply/add a digital signal of their corresponding pixels.
In multiplication, instead of using a microcomputer which is slow, a multiplicity of juxtaposed digital circuits, each being dedicated to multiplication, are usually used to output products that are further subjected to addition. Specifically, let it be assumed that there are two images A, B having pixels in m rows and n columns and that the magnitudes of each pixel signal in the images A, B are represented as being p.sub.ij, q.sub.ij, respectively, as shown in FIG. 2, then, the correlation C of the two images can be calculated by the following equation (1). ##EQU1## Instead of the above calculation, the sum total D in absolute value of differences between the respective pixels can be calculated by the following equation (2). ##EQU2##
In such calculations the respective pixel signals digitized by analog/digital converters 1, 2 are stored in memories 3, 4. And the stored signal data are sequentially applied to a plurality of multipliers 5, 6, 7, 8 by a clock signal for multiplication, and each obtained product is added by an adder 9 so that the sum can be stored in a register 10.
Since the conventional correlation calculators are constructed as described above, their multiplying operation is time-consuming. For realtime operations, the multiplicity of multiplying circuits must be driven concurrently and the products are added thereafter, which requires that the calculators be not only large in structure but also expensive.
The invention has been made in view of the above circumstances. Accordingly, an object of the invention is to provide an inexpensive correlation detector for images which consists of simple circuits and is capable of calculating correlations on a realtime basis.